The invention relates to a spool valve, and more particularly, to a spool valve having an inner hybrid construction and a method of manufacturing the same.
Conventionally, a spool valve provided in a sleeve for switching has been brought into practical use as a directional control valve intended for switching a hydraulic circuit for startup, stoppage, acceleration or deceleration in a hydraulic actuator or the like.
FIGS. 4 and 5 show a typical configuration of such spool valve. In such spool valve, sliding surface portions 11, which form sealing portions between them and a sleeve inner surface (not shown), and ring-shaped grooves 12, which define between them and the sleeve inner surface a passage for a working fluid, are arranged alternately adjacent to each other in a longitudinal direction of the spool valve (see an upper halves of the figures). The sliding surface portions and the ring-shaped grooves are generally integrally formed of a metal, for example, carbon steel (steel type: S45C) or the like (see lower halves of the figures).
Spool valves having such configuration are completed by cutting predetermined lengths of a rod-shaped stock of a desired material, and subjecting the same to many working processes, such as carburization hardening, straightening, centerless, deburring or the like, after machining in accordance with a designed shape. With such conventional spool valves, machining are implemented by a NC machine programmed, which operation requires skill. Further, prior art involves much man-hour for processing of products, and such processes as carburization hardening, straightening or the like, which involve heat treatment take substantial time for treatment. Accordingly, such conventional spool valves are liable to become costly, which makes reduction in manufacturing cost difficult, and there is a limitation on improvement in productivity.